Steering columns are known which collapse to absorb the energy of an axial load imposed on the steering column in the event of a vehicle front end collision. Conventionally, these steering columns dissipate energy through the bending or straightening of metal. For instance, deformable metal brackets used to mount the steering column within the vehicle help absorb energy.
A problem with the use of metal mounting brackets is that they are heavy, and thus add undesirable weight to the vehicle. Furthermore, metal mounting brackets are cumbersome to work with, and constitute one more component which may intrude into the occupant compartment of the vehicle if the front end of the vehicle is driven back during the collision.
As an alternative to heavy mounting brackets, several designs have been proposed in which energy is absorbed through friction between concentric sections of a telescoping steering shaft during collapse. For example, U.S. Pat. No. 3,394,612 to Bogosoff et al, issued July 30, 1968, and U.S. Pat. No. 3,877,319 to Cooper, issued Apr. 15, 1975, both disclose a telescoping steering shaft in which energy is absorbed by the deformation of adjacent concentric sections of the steering column.
Telescoping designs, however, generally have a stroke distance which is limited because the concentric shafts must overlap each other for stability during normal operation. An offset design, in which the steering column has two or more shafts which are joined by a breakaway coupling, requires less of an overlap. Therefore, an offset design can maintain a stroke distance equal to a telescoping design, while shortening the overall length of the steering column. As a result of a shortened steering column, the vehicle dash may intrude further into the occupant compartment without contacting or moving the steering column. Presently, however, many offset designs do not employ any means of energy absorption beyond the point where the coupling between the shafts is broken. In alternative designs such as U.S. Pat. No. 4,718,296 to Hyodo, issued Jan. 12, 1988, the energy absorbed by the steering column decreases as the shafts are displaced relative to each other.